1. Field of the Invention
The present invention relates to methods of generating map update process data, map update methods, and map update apparatuses. More particularly, the present invention relates to a method of generating map update process data, which updates old map data for navigation to new map data, to a map update method, and to a map update apparatus.
2. Description of the Related Art
Navigation apparatuses read out map data corresponding to the current position of a vehicle from recording media, including a compact disc-read only memory (CD-ROM), digital versatile disk (DVD), and hard disk drive (HDD), and display the map data on a display screen. In addition, the navigation apparatuses display a mark of the vehicle at a fixed position on the display screen and scroll the map as the vehicle moves. The map data includes (1) a road layer having node data, road link data, and intersection data, (2) a background layer in which objects on the map are displayed, and (3) a character layer in which, for example, the names of municipalities are displayed. Map images displayed on the display screen are generated on the basis of the background layer and the character layer, and map matching and searching for guidance routes are performed on the basis of the road layer. The navigation apparatuses further have route guidance functions for searching for the guidance routes from departure places to destinations and displaying the guidance routes, and point of interest (POI) display functions for displaying predetermined POI marks (landmarks) on the map.
The map data recorded in the recording media becomes obsolete over time because of changes of topographic data due to, for example, construction of new roads, opening/closing of facilities, land improvement, and others. Accordingly, for example, Japanese Unexamined Patent Application Publication No. 2003-337027 discloses a technology of storing update map data in a non-volatile memory in a navigation apparatus for every block and reading out the maps of blocks where the map data has been updated from the non-volatile memory and reading out the maps of blocks where the map data has not been updated from a recording medium (for example, CD-ROM) to perform navigation control. In this technology, the current map data of the updated block is read out from a removable memory and is written in the non-volatile memory, such as an HDD, in units of meshes, and it is determined whether the update map data of all the meshes in the block is stored in the non-volatile memory by referring to block management information. The map information is read out from the recording medium (for example, CD-ROM) if the update map data of all the meshes in the block is not stored in the non-volatile memory, and the map information is read out from the non-volatile memory if the update map data of all the meshes in the block is stored in the non-volatile memory, in order to perform the navigation control by using the map data. However, with this method, it is necessary to use both the recording medium, such as a CD-ROM or a DVD, and the non-volatile memory, such as an HDD, to perform the navigation control, thus requiring complicated control. In addition, since the recording medium, such as a CD-ROM or a DVD, for recording the map is always required for the navigation control in the technology in the related art, it is necessary to provide a music CD player and a DVD player separately from the map player and, therefore, the hardware is disadvantageously increased in size.
On this account, a method of recording map data in a map recording unit, such as an HDD, and replacing the map data in the HDD with current map data if the map data has been changed is disclosed in Japanese Unexamined Patent Application Publication No. 2004-287705. In this method, a user acquires the difference between the new map data and the old map data from a center or buys an update DVD in which the difference between the new map data and the old map data is recorded to replace the old map data in the HDD with the new map data. With this method, it is possible to perform the navigation control by using the map data recorded in the HDD, to use a DVD player both as the music and video player and the map player, and to listen to the music or watch the video while performing the navigation control.
FIG. 20 schematically illustrates creation of an update DVD with a map differential-data generating apparatus in the related art.
Since the map data is formed of multiple files, the map differential-data generating apparatus (not shown) extracts the difference between a new map file NFL of a new version (Version 2) and an old map file OFL of an old version (Version 1) for every file to generate differential data DFD1 to DFDN. The map differential-data generating apparatus then collects all the differential data to generate update data and writes the update data in a DVD to create an update DVD 1.
FIG. 21 illustrates an update process in a navigation apparatus that uses an update DVD to update old map data in a hard disk to new map data. In the update of the map, a hard disk reading unit 2 in the navigation apparatus reads out an old map file OFL of Version 1 from a hard disk 3 and supplies the old map file OFL to an update processing unit 4. A DVD playback unit 5 reads out differential data from the update DVD 1 and supplies the differential data to the update processing unit 4. The update processing unit 4 uses the differential data and the old map file OFL of Version 1 to generate a new map file NFL of Version 2 for every file. A hard disk writing unit 6 replaces the old map file OFL with the new map file NFL.
However, it takes two hours or more to complete the update of the map in the method disclosed in Japanese Unexamined Patent Application Publication No. 2004-287705, and this method requires a time longer than in a case where the new map file is stored in the DVD from which the new map file is copied to the HDD. This is because it takes a long time to create the new map file from the old map file and the differential data and to read the old map file. As a result, there is a problem in that another music CD or video DVD cannot be listened to or watched for a long time when the update DVD is used in the update of the map.
On this account, a method of writing new map data in a DVD without using a DVD for differential data and directly copying the new map data in an HDD is supposed. However, since the amount of the current map data is around 15 GB, it is necessary to provide two DVDs each having a capacity of 8.5 GB in order to store all the map data. The division of the map data into two DVDs inhibits a background update process from being carried out. The background update process will now be described. When the navigation apparatus performs a navigation process in parallel with a map update process, the navigation apparatus gives preference to the navigation process over the map update process, that is, the apparatus performs the map update process when the navigation process is not performed. The map update process is performed, for example, from the north to the south (a full update process). If the map file of a block where the update has not been completed is requested in the navigation process, the full update process is suspended to update the map data of the block (an occasional update process) and the full update process is resumed after the occasional update process is completed. The navigation apparatus performs the navigation process on the basis of the new map file that is occasionally updated. The above map update process is referred to as the background update process.
However, dividing the map data into two DVDs inhibits the background update process.